The present invention relates generally to a method of preventing refrigerant condensation in a discharge volume or discharge line of a compressor, and, more particularly to the application of one or more heaters to a cooling circuit to prevent condensed refrigerant from migrating into the discharge line and/or discharge volume of a compressor.
Electronic equipment in a computer or telecommunication room requires precise, reliable control of room temperature, humidity and airflow. Excessive heat or humidity can damage or impair the operation of critical computer systems and other components. For this reason, precision cooling systems are operated to provide cooling in these situations.
A typical cooling system 10 is schematically illustrated in FIG. 1. The cooling system 10 includes compressor 20, condenser 30, expansion valve 50 and evaporator 60. Refrigerant for use in the cooling system 10 may be any chemical refrigerant, such as chloroflourocarbons (CFCs), hydroflourocarbons (HFCS) or hydrochloroflourocarbons (HCFCs) such as R-22.
Operation of cooling system 10 is as follows. Refrigerant is compressed in a compressor 20, which may be a reciprocating or scroll compressor or other compressor type. After the refrigerant is compressed, it travels through a discharge line 12 to a condenser 30. A high head pressure switch 24 is attached to discharge line 12. High head pressure switch 24 shuts down the compressor if the discharge pressure exceeds a predetermined level.
In condenser 30, heat from the refrigerant is dissipated to an external heat sink, e.g., the outdoor environment. Upon leaving condenser 30, refrigerant passes through a liquid line solenoid valve 40 and travels through a first liquid line 14 to expansion mechanism 50. Expansion mechanism 50 may comprise a valve, orifice or other possible expansion apparatus known to those of ordinary skill in the art. The expansion mechanism 50 causes a pressure drop in the refrigerant, as the refrigerant passes through the mechanism.
Upon leaving the expansion mechanism, the refrigerant travels through second liquid line 16, arriving at evaporator 60, which comprises a heat exchanger coil. Refrigerant passing through evaporator 60 absorbs heat from the environment to be cooled. Specifically, air from the environment to be cooled circulates through evaporator coil, where it is cooled by heat exchange with the refrigerant. Refrigerant carrying the heat extracted from the environment then returns to compressor 20 by suction line 18, completing the refrigeration cycle.
The precision cooling systems, such as that outlined above for a computer or telecommunications room, are typically operated year round, even when the outdoor ambient temperature is below 40xc2x0 F. Certain operating conditions produce a high head pressure within the cooling system 10 and particularly in discharge line 12. As a result, high head pressure switch 24 shuts down compressor 20 if the discharge pressure exceeds a predetermined level. In particular, when the environment in which the condenser is situated is 30xc2x0 F. or cooler than the environment in which the evaporator is situated (i.e., the environment to be cooled), condenser 30 is significantly cooler than the evaporator.
With the cooling system 10 shut down for an extended period of time, refrigerant is in liquid line expands through evaporator 60 and draws through compressor 20. The refrigerant then condenses in the cold condenser 30. The condenser fills with liquid refrigerant, and refrigerant may begin to condense in discharge line 12 and compressor 20. Starting compressor 20 with liquid refrigerant present in the discharge line 12 and/or the discharge volume of compressor 20 is likely to cause pressure excursion incidents. Condensation-induced shock (CIS) and vapor-propelled liquid slugging (VPLS) are phenomena that can produce dangerous high-pressure excursion incidents in the discharge lines.
To describe the occurrence of CIS and VPLS, operation of cooling system 10 is described after refrigerant has migrated from the liquid lines and condensed in the discharge line 12 and/or discharge volume of compressor 20. During start up of compressor 20, the refrigerant mass flow rate may increase from zero to the normal operating conditions in less than 10 seconds. To transfer momentum to the liquid in discharge line 12, the refrigerant vapor being pumped by compressor 20 undergoes a pressure surge.
Any volume of liquid in discharge line 12 decreases the volume available for the vapor from compressor 20. The less vapor volume available to absorb the pressure surge, the greater is the peak of the pressure surge to provide the necessary transfer of momentum. The condensation in line 12 or the discharge volume of compressor 20 induces a shock or pressure surge. If the vapor discharge volume is too small at startup, the peak of the pressure surge will exceed the predetermined setting of high head pressure switch 24 (which is chosen to prevent damage to the components of the cooling system).
High head pressure switch 24 will trip and shut down compressor 20. Multiple attempts to restart cooling system 10 will eventually result in successful operation. With repeated starts of the compressor, the liquid slugging the line is eventually propelled by the vapor along the line 12, and the volume available to the vapor increases. In other words, the liquid condensate in discharge line 12 can be forced through the line, allowing for enough volume in the discharge line to accommodate the compressed vapor without tripping high head pressure switch 24.
Field reports indicate high-pressure pulses in discharge line 12 in close proximity to the location of pressure switch 24. In some cases this pulse is high enough to peg and bend the needle on the gauge used to perform the measurement. Therefore, damage and wear to compressor 20 and other components of cooling system 10 can result from repeated occurrences of the high head pressure at startup.
It is to be understood that the formation of high-pressure excursion incidents can result from a number of other factors or conditions not listed herein. Furthermore, those conditions cited in the present disclosure as contributing to the possible occurrences of high-pressure excursion incidents may vary with the given design characteristics or installation conditions of a cooling system. The conditions cited are presented as exemplary of those conditions that may lead to high-pressure excursion incidents for a given cooling system in a conventional field setting.
One prior art solution to the refrigerant migration and condensation problem is to move liquid line solenoid valve 40 from the outdoor unit, i.e., condenser unit 30, to the other end of the liquid line 14 just ahead of expansion mechanism 50. Adding a liquid line solenoid valve to all evaporator units in production would prove costly. The circumstances associated with high-pressure excursion incidents as discussed herein occur in only a few installations of cooling system. Furthermore, the problems associated with liquid line slugging and high head pressures at startup are not usually discovered until after installation of a cooling system. Moving or inserting a liquid line solenoid 40 to just ahead of the expansion valve 50 involves a complicated retrofitting procedure. Typically, the procedure involves cutting the liquid line 14 and installing the liquid line solenoid 40 in the new location 42, which can be cost prohibitive.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In view of the foregoing and other considerations, the present invention relates to the application of one or more heaters to a cooling circuit to prevent condensed refrigerant from migrating into the discharge line and/or discharge volume of a compressor.
In accordance with one aspect of the present invention, there is provided a cooling system that includes a first and a second discharge section. The first discharge section includes a discharge volume of a compressor. The second discharge section includes a discharge line, where the discharge line runs from the discharge volume of the compressor to a condenser. The cooling system includes a heating element in thermal communication with at least one of the discharge sections.
In accordance with another aspect of the present invention, there is provided a cooling system. The cooling system includes a first means for collecting a discharge volume of a compressor and includes a second means for communicating the discharge volume of the compressor to a condenser. The cooling system includes a third means for applying heat to at least one of the first or second means.
In accordance with another aspect of the present invention, there is provided a compressor. The compressor includes a discharge section on the compressor and a heating element in thermal communication with the discharge section.
In accordance with another aspect of the present invention, there is provided a method for preventing high-pressure excursion incidents in a cooling system. The method includes the step of heating a compressor discharge volume of the cooling system.
In accordance with a further aspect of the present invention, the method further includes the step of heating a discharge line of the compressor.
In accordance with another aspect of the present invention, there is provided a cooling system having steps for preventing high-pressure excursion incidents in the cooling system. The cooling system includes steps for heating a compressor discharge volume of the cooling system.
In accordance with a further aspect of the present invention, the cooling system further includes steps for heating a discharge line of the compressor.